1. Field of the Invention
This invention relates to an apparatus for bending mainly a long pipe having a small diameter.
2. Description of the Prior Art
A known bending apparatus of this type usually has a twisting unit for holding a pipe and rotating it on its longitudinal axis to predetermine the direction in which it is to be bent, and a bending unit, or units situated on one or both sides of the twisting unit for bending the pipe in the predetermined direction.
When the apparatus is used for bending a pipe at one point after another progressively starting at a point close to one end thereof, however, any previously bent portion of the pipe is twisted again when it is going to be bent at another point. The apparatus has, therefore, the drawback of causing any such bent portion of the pipe to collapse if the pipe has a small wall thickness and a large length. Its use is, therefore, limited to a relatively short pipe having a relatively large diameter and wall thickness.
Another problem is due to the fact that the twisting unit is fixed in position. If the twisting unit has its chuck position not corresponding to the middle portion of a pipe, its chuck position has to be altered; otherwise, the apparatus can be used for bending only a very short pipe.
In order to solve these problems, the applicant of this application has previously proposed a pipe bending apparatus comprising a chuck unit for holding a straight pipe at any point thereof, and a transversely movable bending unitsituated on at least one side of the chuck unit, in which the bending unit comprises a support having a guide groove formed at its top for setting a pipe to be bent, a rotor mounted on the support rotatably within an angle of 360 degrees in a direction perpendicular to the longitudinal axis of the pipe, and having a guide groove formed in its wall surface and similar to the guide groove of the support, a and a motor-driven roller type bending device attached to the rotor rotatably for predetermining the direction in which the pipe is to be bent (Japanese Patent Publication No. Hei 8-9063).
The proposed apparatus, however, fails to achieve a high twisting speed, since its bending unit has a large mass. If the apparatus has to be adapted to bend a pipe to form a plurality of bends having different radii of curvature, its bending unit has a still larger mass, since it is necessary to incorporate in the rotor a mechanism for moving a plurality of bending and clamping dies as required by the bends to be formed. The increase in size or mass of the bending unit results not only in the restriction of the shape of the bend to be formed, but also in a further reduction of the twisting speed. Any forced increase of the twisting speed brings about the vibration of the apparatus which shortens its life and disables it to form an accurately shaped bend.